When strongly heated, orthoboric acid leaves a residue of

Options

A. Metaboric acid
B. Tetraboric acid
C. Boric anhydride
D. Boron

Answer

To solve the question regarding the residue left by orthoboric acid (H3BO3) when strongly heated, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Compound**:
- Orthoboric acid is represented by the chemical formula H3BO3.

2. **Understand the Heating Process**:
- When H3BO3 is heated, it undergoes thermal decomposition. The temperature at which this decomposition occurs is crucial.

3. **Heating at Different Temperatures**:
- At **100°C**, H3BO3 decomposes to form HBO2 (metaboric acid) and water (H2O).
- At **160°C**, it further decomposes to form H2B4O7 (tetraboric acid) and water.
- Upon heating to **red heat** (very high temperatures), H3BO3 decomposes to form B2O3 (boric anhydride) and water.

4. **Determine the Final Residue**:
- The question specifically asks for the residue left when orthoboric acid is **strongly heated**. At red heat, the final product is B2O3.

5. **Conclusion**:
- Therefore, the residue left after strongly heating orthoboric acid (H3BO3) is **boric anhydride**, which is represented by the formula B2O3.

### Final Answer:
When strongly heated, orthoboric acid leaves a residue of **boric anhydride (B2O3)**.

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